Process for tanning leather with waterinsoluble condensation product of a phenol, formaldehyde, and carboxylic acid



'iiatented Oct. 4, less PROCESS FOR TANNTN G LEATHER WITH WATER- ]NSOLUBLE CONDENSATION PRODUCT OF A PHENOL, FORMALDEHYDE, AND CARBOXYLIC ACID No Drawing. Filed Sept. '3, 1958, Ser. No. 158,692

Claims priority, application Germany Sept. 12, 1957 7 Claims. (Cl. 8-94.24)

The present invention relates to and has as its object an improved process for the preparation of leather. The manufacture of leather with the use of synthetic tanning agents containing hydroxyl groups along with mineral tanning agents is known in principle. Thus, it is already known to after-tan chrome-tanned leather with synthetic tanning agents containing phenolic hydroxyl groups which are present in the form of their sulfonic acids salts having only a slight tanning action. These products rapidly acquire their full tanning action through the mineral acids which are present in the chrome leather or set free during the after-tanning, thus changing, especially when used in large amounts for obtaining a good plumpness of the leather, the character of the chrometanned leather towards aleather tanned only with vegetable or synthetic tanning agents. A complete neutralization of the chrome-tanned leather before after-tanning is inexpedient, since it renders the leathers hollow-grained.

It has now been found that leather may be obtained advantageously by tanning a hide obtained in usual manner with mineral tanning agents by known methods and by subsequently treating it with aqueous solutions of alkali metal or ammonium salts of condensation products which contain at the same time phenolic hydroxyl and carboxyl groups and which in the form of their free acids are insoluble or only barely soluble in water. In this case the material is acidified in the liquor, preferably to a pH value at which these condensation products are completely precipitated in the solution. If desired, the process may also be carried out so that a hide is first treated With aqueous solutions of the aforesaid salts, then acidified in the liquor in the indicated manner and, finally, after-tanned with mineral tanning agents in known manner.

The said water-soluble salts themselves exhibit only a slight tanning action or none at all. On the addition of acid, however, they show a more or less marked tanning action, depending on the number of phenolic hydroxyl groups contained in the condensation product, although they are converted at the same time into a waterinsoluble or barely water-soluble form.

The compounds suitable for the process of the invention and present in the form of their Water-soluble alkali metal or ammonium salts are obtainable by known methods. For example, water-soluble salts of known condensation products from phenols or from sulfones of monovalent phenols with hydroxyaryl-carboxylic acids and formaldehyde, or from phenols or phenolic resins with chloromethylated arylor hydroxyaryl-carboxylic acids, or from phenols with aliphatic or aromatic amino-carboxylic acids and aldehydes may be used.

Moreover, phenolic resins in which some hydroxyl groups are etherified with radicals containing carboxyl groups, for example by reaction with chloracetic acid, or

esterified, can also be used in the form of water-soluble salts.

In an expedient way of carrying out the process of the invention, leather tanned in usual manner with mineral, preferably chrome-tanning agents are milled in aqueous solutions of the products according to the invention, and then acidified in the liquor to a pH value of about 26, preferably between 4.5 and .6 by the slow addition .of acid. The addition of acid may be dispensed with, if the leather'has a sufiicient acid reserve. Expediently, .26% of the products to be used according to the invention (referred to the shaved weight of the leathers) are employed. The after-tanning proceeds especially rapidly at an elevated temperature.

By the after-tanning according to the invention, the mineral acid of the leather is combined to a large extent by the tanning agents present in the form of their slightly or non-tanning carboxylic acid salts. Since these tanning agents areconverted by acidification into a water-insoluble or barely water-soluble form, they obtain only a slight tanning action which may be controlled by the addition of acids if desired.

However, this slight tanning action is just suflicient to impart to the leather the desired plumpness, without being so strong, as to change the character of the mineraltanned, particularly chrome-tanned leather to an undesired extent. With the customary use of the synthetic tanning agents containing hydroxyl groups in the form of their sulfonic acid salts, a careful neutralization of the leathers before after-tanning is expedient for the aftertanning of chrome-tanned leathers. With the process according to the invention, this process of neutralization may be dispensed with. The leather obtainable by the process of the invention is moreover distinguished by its softness.

According to another embodiment of the invention the hides obtained in usual manner are milled in aqueous solutions of the products according to the invention. it is thereby advantageous to use those products which exhibit a more pronounced tanning action after the addition of acid. After a brief period of action the tanning efiect of the products is increased by the addition of acid, for example dilute mineral acids. The addition of acid is advantageously continued in portions, until no further precipitates are formed in the liquor. A pH value is thereby reached which is seldom less than 3. The leather is then further tannedin usual manner with a mineral tanning agent. In contrast to the known synthetic tanning agents containing phenolic hydroxyl groups, the synthetic tanning agents according to the invention and containing carboxyl groups andphenolic hydroxyl groups are in most cases completely absorbed by the hide and combined in a water-insoluble form. Tanning agent losses do thus practically not occur, since no tanning agents remain in the liquor. It is therefore possible to add directly the mineral tanning agent, for example an aluminium tanning agent, to these exhausted liquors and to carry out the tanning with the mineral tanning agent by usual methods. In this manner leathers are obtainable, for example with aluminium tanning agents, whose resistance to hot water is appreciably improved, in some cases up to boiling.

The following examples are given for the purpose of illustrating the invention.

Example 1 parts by weight of shaved and nil-neutralized chrome-tanned leather are milled in parts by weight of water at 50 C. and 3-5 parts (referred to solids) of a condensation product from 1 mol of salicylic acid, 2 mols of 4.4-dihydroxydiphenyl sulfone and 3 mols of formaldehyde in the form of its ammonium salt. If

strong precipitates occur from the start of the treatment which are no longer absorbed by the leather, these may be dissolved again by the addition of ammonia. After the treatment, the residual liquor should preferably exhibit a pH value of about 5.5. The leather is worked up in usual manner. Full, grain-resistant, soft and strong- 1y brightened leathers are thus obtained compared with a pure chrome-tanned leather.

Example 2 and 0.75 mol of chloroacetic acid in a known manner. The reaction solution may be used without further puri fication after adjustment to pH 6.5 to 7.

Also leather pretanned in a known manner with a mixture of chromium and aluminium tanning agents may be used according to the above said process.

We claim: i

1. A process for the preparation of leather which comprises subjecting a member selected from the group consisting of a material tanned and to be tanned with mineral tanning agents to the action of aqueous solutions of alkaline salts of condensation products which contain both phenolic hydroxyl and carboxyl groups and in the form of their free'acid are water-insoluble, and acidifying theleather in the liquor to a pH value between 2 and 6 at which the condensation products are completely precipitated in the liquor.

100 parts by weight of squeezed hide are treated and milled in 200 parts by weight'of water. Thereto are added during 8 hours 33 parts by weight of a condensation product from phenol and chloromethyl salicylic acid dissolved in 40 parts by weight of water, and 6.5-10 parts by weight of concentrated ammoniasolution, suitably adding thereby some dilute hydrochoric acid at this stage. After prolonged milling e.g. over night the leather is acidified with dilute hydrochloric acid, until no further precipitates are formed, i.e. until the condensation product is completely precipitated and absorbed by the hide. The liquor has then a final pH value of about 3. The residual liquor is discarded and the leather then milled with a solution of 13.5 parts by weight of aluminium sulfate in 225 parts by weight of water. After 1 /2 hours, the tanning liquor is neutralized with dilute ammonia solution, until no further precipitates or cloudiness occur. The pH value is then 6-65. The leather thus obtained is full, soft and resistant to boiling.

Example 3 100 parts by weight of calf leather tanned with chrome tannins and shaved and neutralized in a usual method and showing a pH value of 4.3 to 4.5 in the cutting are drummed with 4 to 6 parts by weight (solid dry content) of the following condensation product in 150 parts by weight of water of 50 C. During the drumming process an organic or inorganic acid e.g. formic acid or hydrochloric acid is added to keep the pH value of the liquor to 5 to 5.5. The condensation product is taken up by the leather within 30 to 90 minutes according to the method of drumming. The finishing of the leather is carried out in a usual manner. It is possible to combine the drumming process with a fat liquor process using anionic or neutral fat liquors. Also anionic dyestuifs can be used while drumming in the inventive manner. Full and equal leathers are obtained. The condensation product used in this process is obtained by usual methods from one mol of cresol, 0.7 mol of formaldehyde, and by reacting this novolak with 1.2 mols of sodium hydroxide and 0.55 mol of chloroacetic acid.

The solution which is obtained after completion of the v reaction may be adjusted to pH 6.5 to 7 and used without further purification.

Another condensation product which may be used is obtained by reacting a novolak of 1 mol phenol and.0.6 mol of formaldehyde with 1.6 mol of potassium hydroxide 2. A process for the preparation of leather which c0mprises subjecting a mineral-tanned leather to the action of aqueous solutions of alkaline salts of condensation products which contain both phenolic hydroxyl and carboxyl groups and in the form of the free acid are Waterinsoluble, and acidifying the leather in the liquor to a pH value between 2 and 6 at which the condensation products are completely precipitated in the liquor.

3. Process of claim 1 wherein said salt is an alkaline salt of a condensation product of monohydric, monocyclic phenols and formaldehyde, in which the free hydroxyl groups are partially etherified by CH COOH-gI'OUPS.

4. A process of claim 1 wherein said salt is an alkaline salt of a condensation product of salicylic acid-4.4'-dihydroxy diphenyl sulfon and formaldehyde.

5. An improved process for the preparation of leather which comprises milling an acidic chrome-tanned leather in an. aqueous solution of a condensation product prepared from 1 mol of salicylic acid, 2 mols of 4,4-dihydroxydiphenylsulfone, and 3 mols of formaldehyde, said condensate being added in the form of its ammonium salt, maintaining the acidity of said aqueous solution at a pH of 2-6 until the condensation product is completely precipitated and recovering a soft and strongly brightened leather.

6. An improved process for the preparation of leather which comprises milling a hide in an aqueous solution of a condensation product of phenol and chloromethyl salicylic acid, maintaining the acidity of the solution at a pH of 2-6 until the condensation product is completely precipitated and absorbed by the hide, discarding the residual liquor, and then milling the leather in an aqueous aluminum sulfate solution, after which the tanning liquor is neutralized and a full, soft leather obtained.

7. An improved process for the preparation of leather which comprises drumming chrome-tanned leather in a treating solution containing a condensation product prepared by reacting a oresol-formaldehyde novolak with sodium hydroxide and chloroacetic acid, and maintaining the acidity of the treating liquor at a pH of 26 at which the condensation products are completely precipitated in the liquor.

References Cited in the file of this patent UNITED STATES PATENTS 1,989,802 Hester et al. Feb. 5, 1935 

1. A PROCESS FOR THE PREPARATION OF LEATHER WHICH COMPRISES SUBJECTING A MEMBER SELECTED FROM THE GROUP CONSISTING OF A MATERIAL TANNED AND TO BE TANNED WITH MINERAL TANNING AGENTS TO THE ACTION OF AQUEOUS SOLUTIONS OF ALKALINE SALTS OF CONDENSATION PRODUCTS WHICH CONTAIN BOTH PHENOLIC HYDROXY AND CARBOXYL GROUPS AND IN THE FORM OF THEIR FREE ACID ARE WATER-INSOLUBLE, AND ACIDIFYING THE LEATHER IN THE LIQUOR TO A PH VALUE BETWEEN 2 AND 6 AT WHICH THE CONDENSATION PRODUCTS ARE COMPLETELY PRECIPITATED IN THE LIQUOR. 